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Full text of "Handbook Of Chemical Engineering - I"

POWER GENERATION AND TRANSMISSION
65
of quantity or strength.   The following table illustrates the same characteristic as the chart.
RELATIVE   INCREASE OF FUEL CONSUMPTION PER B.Hp.  PER HOUR
LOADS
	Full-load	% load	Kload	k   -
Natural-gas engine ..........	1.00	1 05-1 20	1 20-1 50	1 75-2 0<
Illuminating-gas engine ........	1.00	1.05-1.20	1 20-1 50	1 75-2 ~
Producer-gas plant (engine and producer)	1.00	1 15-1 25	1 45-1 60	2 30-S
Gas producer      .......	1.00	1.04-1.06	1 10-1 15	1 30-1
Blast-furnace gas engine .....	1.00	1 . 05-1 . 20	1 20-1.50	1.75-2
				
(From MARKS' Mechanical Engineers1 Handbook;
Losses.—The chief heat losses in gas engines are those to the jacket water and the exhaust: each of these losses is roughly equal to the heat converted into power. The jacket water outflow temperature is rarely above 160°, so that this
HEAT BALANCES OF GAS AND OIL ENGINES (Per cent of heat of combustion.—Lucke, "Thermodynamics")
Engine	I.hp.	B.hp.	Friction"	Jacket	Exhaust	Radiation and unaccounted for
General (Mathot) .......	33 0	28 0	5 0	36 0	31 0&	
300-hp. engine at 197 lip ..... 300-hp. engine at 294 hp ..... 300-hp. engine at 335 hp .....	43.5 45.8 41.5	33.5 32.2 30.9	10.0 13.6 10.6	34.3 31.8 33.8	24.1 23.9 24.8	1.9C 1.5' 0.1'
"Including pump work.    ^Including radiation, etc.    cExcess.
heat is largely unavailable for further use. If the water is clean, some of it may be used for boiler feed or for heating processes: or its temperature may be increased to fit it for warming buildings or for process work. The exhaust gas temperature is 600 to 700°, but the gases part with their heat at a slow rate, since dry gas is a poor conductor. Devices for transferring this heat to water, steam, etc., must therefore have ample surface.
Details.—Ignition is now universally electrical. Large engines employ low-tension direct-current mechanical make and break. High-tension jump-spark ignition is used for smaller sizes. The ignition should usually start at the center of the combustion space, but in large cylinders a plurality of igniter electrodes will be required. Starting is by hand, by motor geared to the flywheel, or by compressed air. Air-cooling is used only for very small engines. The cooling water required is about 10 gal. per brake horsepower per hour. From 10 to 20 Ib. water pressure is sufficient unless pistons are cooled (double-acting